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UC Berkeley researchers have developed a method to provide real-time, high-resolution data in hard-to-map waterways, using GPS. Tossing a robot is Andrew Tinka, with Kevin Weekly. (Photo courtesy of Jérôme Thai.)

By Tracy Cozzens

A fleet of 100 robots equipped with GPS and sensors were released May 9 into California rivers to measure water flow, salinty levels, and pollution. The Floating Sensor Network is a project by the University of California, Berkeley, to improve the way water quality and flows are monitored.

About two-thirds of California’s fresh water is in the Sacramento-San Joaquin river system where the test took place. This water supplies about two-thirds of the state’s population with drinking water and irrigation. The initiative is led by associate professor Alexandre Bayen at the Center for Informatin Technology Research in the Interest of Society (CITRIS).

The robots each have a sensor to test salinity and a GPS unit from a smartphone. Some have propellers so they can maneuver around obstacles and reach specific destinations. The robots also sent Tweets to @fsnandroid61.

The robots drifted through the area of the river being measured, then were retrieved by boat. “One advantage of our real-time communication system is that we can see where all our sensors are on a map, which makes it very easy to chase them down and retrieve them,” said graduate student researcher Andrew Tinka.

With the first test completed, the team’s efforts over the summer have two priorities, Tinka explained. “First, we’re using the flow data that we gathered on May 9 to understand how this ‘mobile’ data can be best used for river hydrodynamics studies. We’re learning how to turn the individual traces of water that each sensor gives us into a big-picture view of the entire river region, sort of how like meteorologists take the data from a few weather stations and turn it into an overall view of what the weather is doing over a large area. Second, we’re working with other hydrodynamics research groups to expand the use of this kind of mobile sensor. We’re loaning our equipment to other groups, doing pilot projects with others, and basically trying to get these sensors into researchers’ toolboxes throughout the water community.”

There are two types of devices in the fleet, active and passive. The active sensors have a twin-propeller drive system that lets them move through the water to avoid obstacles or stay in the correct region of the river. “We developed the internal electronics for this device ourselves,” Tinka said. “We integrated a Magellan AC12 GPS receiver along with a Gumstix embedded computer and a Motorola GSM module. Our passive sensors don’t have a propulsion system; they do exactly what the water does. We developed this system with a focus on cost and ease of assembly.” The team used a waterproof consumer smartphone, the Motorola Defy, for the GPS positioning, computation, and comunications.

So far, the test has proven the usefulness of such a network. The devices were developed to be easily deployable, especially where a lot of flexibility is needed, such as in disaster response. “The ability to quickly and easily put these sensors into new inland environments, by just about any method (throw them from a boat, drop them from a helicopter, toss them from a dock or a bridge) makes them a really useful new tool,” Tinka said.

A hundred robots, 40 with propellers, were released into the Sacramento River near Walnut Grove (photos courtesy of Jonathan Beard).